Method and apparatus for operating underground storage caverns



v-r H Jan. 20, 1959 'R. M. GIBSON ET AL 2,869,328

METHOD AND APPARATUS FOR OPERATING UNDERGROUND STORAGE CAVERNS Filegi Oct. 12, 1953 m U TED EE/NE' FEES WATEZZ HYDEOCA 250 M2 H Y-DEOCAFEO/V United States Patent METHOD AND APPARATUS FOR OPERATING UNDERGROUND STORAGE CAVERNS Robert M. Gibson, Sour Lake, and Karl C. ten Brink and Austen M. Shook, Houston, Tex., assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application October 12, 1953, Serial No. 385,590

7 Claims. (Cl. 61-.5)

The present invention relates to a novel method of and apparatus for operating an underground storage cavern wherein the fluid being stored is introduced into the cavern while displacing a highly concentrated water solution therefrom. The invention has particular application to operating an underground storage cavern formed in a salt bed or dome hundreds of feet beneath the surface of the earth, from which a highly concentrated sodiumchloride brine is displaced as butane or other hydrocarbon liquid is forced into the cavern.

Underground storage of butane and other hydrocarbon liquids in salt caverns has recently become important in petroleum technology, and has been adopted widely. One problem encountered in this storage method has been that as the butane or other fluid to be stored displaces highly concentrated or saturated brine from the cavern to a temperature of about 112 F. When this brine reaches the surface of the earth its temperature may be reduced to 80 F. The aqueous solubility of sodium chloride at 112 F. and a pressure of 1 atmosphere is 36.77 grams tion a short distance above the surface 13. Within the casing 17 is concentrically located a long central conduit 21 having its lower end 23 located adjacent the bottom of cavity 11, and extending at its upper end through -a pool 33 of highly concentrated brine.

casing 17 to a section 25 a short distance above the surface 13.

When introducing the hydrocarbon or other fluid to be stored into the cavity 11 it is forced by a pump or by its own vapor pressure through a supply conduit 27 controlled by a valve 29 into the casing 17 and down into the cavity to form a pool 31 floating on the top of A fluid enters through conduit 27 the level of the brine 33 is forced down and displaced brine enters the central tube 21 through perforations 32 in its side wall near its lower end 23, flows up through tube 21 into its section 25, through a control valve 35, and thence to a storage reser- As the brine flows up through tube 21 in countercurrent heat exchange relationship with the incoming cool hydrocarbon its temperature and pressure are gradually reduced as it approaches the surface 13, and some pre cipitation of salt may occur. When the brine reaches the section 25 above the surface, there is a further reduction in temperature and precipitation of salt in the V conduit section 25 ordinarily may occur to such an per 100 grams of Water; and at 80 F. is only 36.19

grams per 100 grams of water. The solubility difierence is even greater because of the higher pressure in the cavern, of the order of 400 pounds per square inch.

In accordance with the present invention when operating an underground storage cavern wherein the flow into the cavern of the fluid to be stored, such as butane, is accomplished by displacement of a stream of a highly concentrated water solution, such as sodium chloride brine, at a relatively high temperature through a discharge conduit having an inlet in the cavern and a section at a relatively lower temperature, the problem of solute precipitation in the discharge conduit is solved by introducing a flowing stream of solvent such as relatively fresh diluting water into the discharge conduit at a point between its inlet and the lower temperature section to reduce the concentration of solute and thereby substantially prevent solute from precipitating.

The invention will be described more in detail below, with reference to the accompanying drawings, wherein:

Figure 1 is a schematic vertical sectional view, parts being in side elevation, showing an underground storage cavity and its associated equipment; and

Figure 2 is a schematic vertical sectional view, parts being in side elevation, showing a similar underground storage cavity with a modified form of associated equipment. 7

As shown in Figure 1, an underground storage cavity 11 is located hundreds of feet beneath the surface 13 of the earth in a salt bed or salt dome. Cavity 11 is provided with an access bore 15 lined with a casing 17 which extends from the top 19 of the cavity to a posiextent as to clog the conduit. Precipitation may also be caused by the agitation imparted by valve 35.

To eliminate salt precipitation there is provided a conduit 37 controlled by a valve 39 which opens into and supplies relatively fresh water continuously to the section 25 in such volume as to dilute the brine so that the concentration of salt is reduced below the saturation value, at which salt may precipitate out of solution. As an example, precipitation clogging has been prevented by supplying fresh water at a rate of about 2 gallons per 42 gallon barrel of saturated brine flowing.

The problem of salt precipitation in the part of conduit 21 within the earth is not as severe as in section 25. However, in time even this may become clogged with salt. Therefore, periodically the valve 35 is closed while the valves 29 and 39 are allowed to remain open, with the result that fresh water from conduit 37 flows down through the conduit 2-1 to its lower end and re moves the deposited salt both by dissolving it and mechanically washing it free fromthe walls. Hydrocarbon at the same time flows back through conduit 27. In one example of how the conduit 21 is flushed out, fresh water is injected in an amount equal to twice the volume of the conduit, which is then left standing full of fresh water until fluid flow into the cavern through supply conduit 27 is resumed after reopening valve 35.

In the embodiment illustrated in Figure 2 the fluid to be stored is introduced through a conduit 27' to a casing 17 to form a pool 31' floating on a pool of saturated brine 33 as described in connection with Figure 1. As fluid enters the cavern brine is displaced up through a central conduit 21 and thence through a section 25 to a disposal reservoir. In this modification, relatively fresh diluting water is injected continuously through a supply conduit 55 controlled by a valve 47 and extending down through the conduit 21 to a position 49 adjacent its lower end. Consequently, fresh water reaches the lower end of conduit 21 adjacent the point where brine enters the conduit and dilutes the brine below the saturation value so that no precipitation of salt will occur in any part of the conduit 21'. With this construction and mode of operation it is usually unnecessary to flush out the conduit 23. periodically, as described in connection with Figure 1. However, any unusual deposition of salt in conduit 21' can be re- Patented Jan. 20, 1959 been removed, after which valve 29 is reopened to resume normal operation.

Obviously, many modifications and variations of the invention, as hereinbeforeset forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. in a method for operating an underground storage cavern wherein the flow into said cavern of the fluid to be stored is accompanied by the displacement of a stream of a highly concentrated solution of solute in liquid at a relatively high temperature out of said cavern through a conduit having an inlet in said cavern and a section at a relatively low temperature in which solute normally precipitates out of solution and accumulntes on the Walls of said conduit, the improve-.

ment which comprises introducing a flowing stream of diluting liquid into said conduit at a point between said inlet and said section to reduce the concentration of solute in said solution and thereby substantially prevent solute from precipitating out of solution at said relatively low temperature, whereby to prevent clogging of said conduit by precipitated solute.

2. In a method for operating an underground storage cavern wherein the flow into said cavern of the fluid to be stored is accompanied by the displacement of a stream of highly concentrated brine, out of said cavern through a conduit having an inlet in said cavern and a section adjacent the surface of the earth in which salt normally precipitates out of solution and accumulates on the walls of aid conduit, the improvement which comprises introducing a flowing stream of diluting water into said conduit between said inlet and said section in suflicient volume to reduce the concentration of salt in said brine below the value at which salt precipitates out of solution, whereby to prevent clogging of said conduit by precipitated salt.

3. In a method in accordance with claim 2, introducing said stream of diiuting water into said conduit adjacent said inlet whereby the entire length thereof is kept free from precipitated salt.

a PAEFIZQQJIL S99$12Q wi h. la ms 2 ntro; ducing said stream of diluting water into said conduit adjacent the surface of the eaith.

5. In a method in accordance with claim 1, the additional steps of periodically stopping the flow of solution from said cavern, and flushing out with diluting r/ he; part'ofsai conduit between said inlet and said point torernoyeany precipitated solute therefrom.

6. In a method in accordance with claim 5, flushing out said conduit by forcing said diluting water to flowtherein in a direction opposite to the flow of solution therethrough.

7. Apparatus for operating an underground storage caverntcoinprisingv'a, first conduit extending from the surface down into such a cavern for introducing therein the fluid to be stored; a second conduit extending from said cavity to the surface for conducting from said cavity a liquid, control solution displaced by said fluid, said second conduit having an inletin said cavern and a section adjacent said surface wherein the temperature of said solutionvis lowerv than in saidcavern; and a third co nduit opening into said second conduit near said surface for supplying diluting water to said second conduit in sufficient volume to reduce the concentration of solute in said control solution below the. value at which precipitation occurs.

References ,Cited in the file of this patent UNITED STATES PATENTS 691,975 Schaaf Jan. 28, 1902 1,449,754 Hulsmeyer Mar. 27, 1923 1,636,455 Blumenberg July 19, 1927 2,361,231 Nebolsine Oct. 24, 1944 2,590,066 Pattinson M Mar. 18, 1952 2,747,774 Breitenbach May 29, 1956 OTHER REFERENCES 

